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Managing Hydrangeas: To Prune Or Not To Prune And Other Existential Questions

To prune or not to prune? That is one of the quintessential gardening questions. Recently I asked a top landscaper in Virginia to weigh in on the issue. “When is the best time to prune hydrangeas without cutting off next year’s flowers?” I asked. Her reply?

“Never,” she said with a laugh. “But your best shot is after they’ve bloomed.”

It turns out that knowing how and when to prune hydrangeas involves first, identifying what kind you own. It all starts with determining whether your hydrangeas flower on old or new wood.

HYDRANGEAS THAT BLOOM ON OLD WOOD

Nikko Blue hydrangeas bloom on old wood

Old wood is quite simply, last year’s wood. Hydrangeas that bloom on old wood set their flower buds on stalks that have been on the plant since last summer. This generally occurs sometime in August, September or October.

Hydrangeas that bloom on old wood include the Mophead, Big Leaf and Lacecap types as well as Oakleaf varieties. These are the kinds of shrubs that, until recently, were most commonly found in gardens.

Oakleaf hydrangea is recognizable by its foliage that resembles oak leaves

Knowing when and what to prune is key to protecting next year’s blooms on these magnificent plants. Most importantly, the more old wood you take, the less of a floral display there will be next summer. As a rule, these shrubs need little pruning. But if you must, your hydrangeas will thank you if you follow these simple steps:

Immediately after flowering and no later than July, remove flowering stems back to a pair of healthy buds.

Prune out weak or winter-damaged stems in later winter or early spring by cutting out no more than 1/3 of the oldest stalks, taking them down to ground level.

Repeat the process every summer to rejuvenate the shrub and control its shape.

HYDRANGEAS THAT BLOOM ON NEW WOOD

Limelight hydrangeas bloom on new wood

Hydrangeas that bloom on new wood set their flowering buds on the current season’s growth. Because their flowers come from new growth from the base of the plant, they can be pruned almost any time of year, except summer. Most gardeners recommend pruning these types of hydrangeas in the late winter or very early spring when you can best see the branch structure.

Hydrangea arborescens ‘Annabelle’

Considered the crème de la crème of all the varieties that bloom on new wood, Hydrangea arborescens Annabelle is what is called a ‘smooth’ hydrangea. Smooth hydrangeas are known for their giant white blooms and are native to the southeastern United States.

Distinctive white blooms of Hydrangea ‘Annabelle’

What makes Annabelle so special is that it not only produces enormous, pure white blooms from June to August, but also stays compact, growing to just 3 to 5 feet tall and wide. At first glance, it can be hard to tell this cultivar apart from other white-blooming hydrangeas. However, a number of gardeners go by this golden rule: Annabelle flowers open lime green in early summer, change to bright white mid-summer and then switch back to light green in late summer before turning tan in the fall.

More recently, an improved version of Annabelle called Incrediball has been developed. It features basketball-sized blooms and thicker, sturdier stems that don’t flop over even if the flower heads become soaked with rain.

‘Incrediball’ features 12″ flower clusters and blooms on new wood

To control for shape and increase blooms, some gardeners cut their Annabelle hydrangeas back to the ground (within 6″) in late winter or early spring. Some say this encourages the shrubs to produce the largest flowers and sturdiest stems. On the other hand, others say it weakens the plants over time, causing them to need to be staked. I recommend taking the middle road and cutting Annabelles back to between 1 and 3 feet above the soil.

Panicle hydrangeas

Panicle hydrangeas bloom on new wood

Panicle hydrangeas (Hydrangea paniculata) also bloom on new wood. Like Annabelles, they can be pruned in late winter or early spring. Cut them to the ground or to just a few feet above the soil depending on the size plant you want to maintain. The best known of the panicle hydrangeas include PeeGee and Limelight.

When they were first introduced from Holland in the early 2000’s, Limelight hydrangeas took the garden world by storm. Featuring enormous, football shaped clusters of flowers, the shrubs performed great in full sun (although for best color, they require some shade). Limelights keep their beautiful celadon color all summer long before aging slowly to pink and finally shades of dusty red and burgundy in the fall.

Limelight hydrangeas bloom on new wood

ENDLESS SUMMER IS THE BEST OF BOTH WORLDS

There’s a new kind of hydrangea in town called Endless Summer and it’s rocking the hydrangea world. Introduced in 2004 by Bailey Nurseries, Endless Summer hydrangeas bloom on both old and new wood. As a result, this gives them the ability to flower repeatedly all summer. The company’s tag line is, appropriately,

Experience life in full-bloom.

Endless Summer mophead variety

As of 2018, there are three different varieties currently available. Blushing Bride produces pure white mophead flowers that mature to soft pink. Twist-n-Shout is the first re-blooming lacecap variety. And BloomStruck has vivid purple or rose-pink mophead blooms that hold their color all summer. Summer Crush (available in 2019) will feature raspberry red or neon purple blooms.

It’s easy to imagine the benefits of plants that bloom on both old and new wood. Their flowers naturally last for most of the summer. Moreover, the company says Endless Summer hydrangeas bloom 10 to 12 weeks longer than average hydrangeas.

SOME COMMONLY ASKED QUESTIONS ABOUT HYDRANGEAS

Why are my hydrangea flowers turning brown in the summer?

The main reason that mophead flowers turn brown is too much sun; specifically hot mid-day to afternoon sun. To prevent this problem, site your shrubs in areas where they receive direct sun either in the early morning or late afternoon. Same goes for the lacecap varieties, which tend to have a much shorter flowering span than the mopheads. Attention to watering during dry spells also helps prolong blooms.

What do I do if my hydrangeas have grown too big and floppy?

Most gardeners advise waiting until the shrubs have been in the ground for 5 years before beginning a pruning program. If you’ve got the type that blooms on new wood, prune your shrubs in late winter or early spring for shape, taking them down to between 1 and 3 feet from the ground. If you’ve got the kind that blooms on old wood, follow the method above, removing 1/3 of the oldest living stalks each summer after the shrubs have flowered.

When I cut blossoms will it hurt the other blooms?

After August, cut only short stems to avoid affecting next year’s blooms

For hydrangeas that bloom on old wood, deadheading (or cutting flowers for indoor arrangements) can be performed on long or short stems in June through July without affecting next year’s flower buds. After August, it’s best to harvest only short stems.

Can I prune some of the branches and not affect others?

Yes. You are only cutting off the flower buds on the stalks that you prune.

Does watering keep the blooms going? Why do my hydrangeas look so dry in July?

As with all plants, watering during dry spells is key. Keep the soil moist around your hydrangea shrubs to keep the flowers going all summer.

I did all the right things and my hydrangeas didn’t bloom this year. What happened?

Weather can negatively affect blooms, too

Finally, you can follow all the rules and prune your new or old wood shrubs correctly, but weather can also have its negative effects, particularly frost. In colder regions, flowering can be adversely affected by either early fall or late spring frosts, making it confusing as to whether you pruned off the blooms yourself or left it to Mother Nature.

About carole funger

I'm a garden designer and Maryland Master Gardener living in the Washington, DC area. I blog about new trends in horticulture, inspiring gardens to visit and the latest tips and ideas for how to nurture your own beautiful garden. Every garden tells a story. What's yours?